Abstract

Approximately 20,000 km2 (7900 mi2) of three-dimensional (3-D) seismic data, along with the Bouguer gravity and bathymetry, show a series of intraslope lineaments that extend more than tens of kilometers (miles) in the Lower Congo Basin, offshore Angola (west Africa). Most of these lineaments trend to the northeast at approximately 45°, crossing the regional northwest-trending folds and thrusts. Geometric relationships and distribution patterns of folds and faults shown in the postsalt Tertiary section suggest that many of the lineaments might have a significant strike-slip component. Seismic structures, facies, and prospects indicate that the lineaments have been associated with the allochthonous salt bodies, turbidite sands, and oil and gas fields. We interpret that the lineaments are primarily related to the postsalt regional gravitational sliding of the Tertiary sediments. They could provide fairways for turbidite flow and pathways for salt emplacement and hydrocarbon migration. We infer that many cross-regional lineaments are the expression of the presalt basement transfer faults formed during the rifting phase of the continental crust in the Early Cretaceous have influenced the locus and orientation of the lineaments in the postsalt sediments. The obliquity of the continental lineaments (45°) to the oceanic fracture zones (80°) is consistent with and supportive of the previously recognized plate tectonic model depicting the counterclockwise rotation of the west African continent associated with the southward opening of the South Atlantic Ocean. These findings provide important insights to the nature of the cross-regional lineaments and their implications for tectonics, sedimentation, and petroleum systems at the west African passive continental margin.